So I'm saving overall about 20% of the space required which isn't bad for a directory that contains a lot of images and PDFs.

Handily, HFS Compression being very low level plays nicely with pretty much everything else except anything to do with developer tools - for some reason it really doesn't like compressing .c source code files.

So you can combine this with Dropbox to save some local space for all those important files that you don't need very often.